Traditional incandescent lighting devices are currently being replaced by more energy efficient solid state based light sources, such as light emitting diode (LED) based light sources. Solid state based light sources have significantly different optical characteristics compared to incandescent light sources. In particular, solid state based light sources provide a more directed light distribution and a higher (i.e. cooler) color temperature compared to incandescent light sources. Therefore, efforts have been made in order to make solid state based lighting devices to better resemble traditional incandescent lighting devices in terms of light distribution and color temperature.
Wavelength converting material, such as phosphor, is normally used to adjust the color temperature of light emitted by light sources. The wavelength converting material may be positioned directly on the light source or in a separate element spaced from the light source, the latter normally being referred to as a remote wavelength converting element.
US 2012/0176804 shows a lighting device comprising an LED emitting ultraviolet (UV) light, which is converted by phosphor into visible light (such as white light). The phosphor is disposed at a light guide, which is a planar panel disposed above the LED such that the majority of the light emitted by the LED strikes the panel. The light guide and the LED are covered by an envelope. A drawback with such a lighting device is that it may be difficult to manufacture if the light guide is larger than the bottom opening of the envelope. It may e.g. require that the envelope is made in two pieces or that the light guide is made in a flexible material.